The object invention relates to dentistry equipment, in general, and to a mixing and storage assembly for ceramic materials such as dental porcelain, in particular.
Heretofore, difficulty has been encountered in maintaining the proper moisture content of dental porcelain during its use and storage. Frequently used for dental restorative work, porcelain is a hard, white, translucent and non-porous ceramic material known for its bio-compatability and corrosion-resistant properties. Dentists and other professionals who use this material for the fabrication of dentures, pontic or crowns, for example, typically purchase it in the form of a powder to be admixed with water or other suitable liquids.
Because the workability of the mixture is a direct function of its "wetness", it is important to maintain the proper moisture content during use and storage. It is well known to those skilled in the art of dental restorative fabrication, however, that the porcelain mixture rapidly commences to harden or "set" after preparation due to water loss through evaporation. During use, it is common practice to add water or other liquid to maintain the mixture in a workable state. Failure to do so often results in mixture discoloration and reduced strength of the restorative.
Efforts to maintain the mixture's proper moisture content during both use and storage have been met with limited success. One example is described in U.S. Pat. No. 4,180,159 issued Dec. 25, 1979 to Tanaka which teaches a tray assembly for mixing the porcelain material and subsequently maintaining its moisture content. The tray assembly includes a receptacle for mixing and supporting the mixture and an underlying reservoir for storage of water or other liquids. One end of an elongated wick is immersed within the liquid and the opposite end of the wick is disposed in the receptacle and in contact with the product therein. While the liquid is, in fact, drawn via the wick from the reservoir to the mixture, the invention of Tanaka has been criticized for failing to provide sufficient amounts of water to the substrate. This is probably due to the relatively small portion of the wick end which contacts the mixture or perhaps due to restricted liquid flow when hardened mixture residue accumulates on the wick tip causing blockage.
Another earlier invention described in U.S. Pat. No. 3,966,094 issued Jun. 29, 1976 to Sheppard teaches an apparatus having a porous working surface for supporting a castable material again disposed above a reservoir filled with liquid. A flow of liquid is maintained from the reservoir through the porous working surface to the mixture through hydrostatic pressure as a function of liquid elevation within one or more wells. Despite the potentially large amount of water which can be stored in the Sheppard device, once water elevation ceases to make contact with the working surface, moisture loss from the mixture can not be prevented. Moreover, as the water level within the reservoir decreases due to evaporation, the hydrostatic pressure changes resulting in an inconsistent flow rate to the substrate. Accordingly, water level must be frequently checked and maintained to avoid substrate moisture depletion or supersaturation. It is also worth noting that the Sheppard device is not equipped with a lid and is not, therefore, intended for more long term storage of the porcelain mix.
It is clear that a significant need exists for a solution to the shortcomings and limitations of the above described inventions as well as those of other prior art efforts attempting to control moisture content in the dental porcelain mix. The subject invention substantially obviates the problems associated with the prior art by providing a means for regulating moisture content within the substrate mix during both use and storage. Liquid flow to the mix is kept relatively constant over time by exploiting the capillary action inherent in both the subject device and in the mixture itself.